Micromanipulator

ABSTRACT

A micromanipulator comprises a pair of hand modules each of which includes a circular base plate with three connection points, an end-effector consisting of a circular moving plate and a finger attached to the moving plate, the moving plate being disposed above the base plate and having three connection points offset 60 degrees from those of the base plate, six metal links disposed between the base plate and the moving plate, six actuators provided on the six metal links for extending and contracting them, six first metal wire members connected between one end of the six metal links and the three connection points of the base plate so that two wire members are connected with each connection point of the base plate to be inclined in opposite directions, and six second metal wire members connected between the other end of the metal links and the three connection points of the moving plate so that two wire members are connected with each connection point of the moving plate to be inclined in opposite directions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a micromanipulator adapted for use in fieldsrequiring precise positioning on the μm order, particularly for use inthe integrated circuit (IC) industry (for precision wafer positioning),bioengineering, medicine (microsurgery), satellite communications(precise antenna positioning) etc.

2.Description of the Prior Art

Micromanipulation is the technology of conducting operations on minuteobjects (for example, cells) with sizes on the order of several tens ofμm. It can be effectively applied, for instance, for grasping a minuteobject with two fingers and positioning it by translational androtational motion, as well as for operations such as gripping, pressing,cutting, stretching, compressing, perforating, mixing and propelling. Assuch, it has become an indispensable technology in a wide range offields including biotechnology and medicine. However, since most of themicromanipulators that have become commercially, available up to thepresent consist of a combination of a mechanism for translational motionin three mutually perpendicular directions and a gripper, they are notoptimally adapted for use with microscopic objects.

In view of these circumstances and in light of the fact that in themicroworld surface forces are dominant over inertial force, the inventorconcluded that a two-finger microhand would be capable of sufficientlystable micromanipulation. He therefore developed a two-finger hand witha drive mechanism utilizing parallel linkages with six degrees offreedom (DOF). This micromanipulator, which is described in JapanesePatent Application Hei 3(1991)-305,220, was confirmed to be highlyeffective as regards operability, controllability and the like.

This earlier proposed micromanipulator is constituted as a two-fingerhand employing a pair of hand modules with 6-DOF parallel linkages. Eachhand module has a base plate and an end-effector consisting of a movingplate and a finger attached to the moving plate. The base plate and themoving plate are connected by six links that are extended and contractedby piezoelectric actuators. The six links are divided into two groups ofthree each. The links of both groups are connected with the base plateand the moving plate at points spaced along circles whose centers arethe axial centers of the plates, but the links of one group are inclinedin the opposite direction from those of the other group. Since the needfor the micromanipulator to be compact makes it difficult to use balljoints or the like for connecting the links with the base plate and themoving plate, the connection is made by pivots and springs connectedbetween the base plate and the moving plate for retaining the links in asqueezed state between the base and moving plates.

Although this configuration is highly effective from the viewpoint ofreducing the size of the micromanipulator, various tests conducted on aprototype configured in line with this design revealed shortcomings.First, since the links are held between the base plate and the movingplate of the end-effector by spring force, the micromanipulator isliable to break down structurally when exposed to an external forceexceeding the spring force. Second, since the springs constitute avibration system, the micromanipulator cannot be used in the naturalfrequency range of the vibration system determined by the springconstant and the mass of the vibrating members and is further unable tofollow rapid movements with adequate response. From the test results itwas concluded that configurational improvements for coping with theseproblems would enable realization of a practical micromanipulator.

The present invention was achieved in light of the foregoing findingsand has as its object to provide a micromanipulator which is strongenough not to structurally break down easily under external force andwhich, not having a spring vibration system, is able to follow rapidmovements with good response.

SUMMARY OF THE INVENTION

The invention achieves this object by providing a micromanipulatorconstituted of a pair of hand modules each comprising:

a circular base plate provided along its edge with three substantiallyequally spaced connection points,

an end-effector consisting of a circular moving plate and a fingerattached to the moving plate, the moving plate being disposed above thebase plate and being provided along its edge with three substantiallyequally spaced connection points offset about 60 degrees from theconnection points of the base plate,

six metal links disposed between the base plate and the moving plate,

six actuators provided one on each of the six metal links for extendingand contracting the metal links,

six flexible first metal wire members each connected between one end ofone of the six metal links and one of the three connection points of thebase plate, two first metal wire members being connected with eachconnection point of the base plate to be inclined in differentdirections from each other, and

six flexible second metal wire members each connected between the otherend of one of the six metal links and one of the three connection pointsof the moving plate, two second metal wire members being connected witheach connection point of the moving plate to be inclined in differentdirections from each other.

When selected links of the hand modules of the so-configuredmicromanipulator are extended/contracted by operating the associatedactuators, the positions and directions of the end-effectors arecontrolled with six degrees of freedom according to the amount of linkcontraction, whereby the fingers of the micromanipulator can be causedto execute prescribed motions.

Further, since the connection of the links with the base plate and theend-effector is made at the connection points by direct coupling usingflexible metal wire members, the micromanipulator is strong enough notto structurally break down easily under external force and, moreover,since it has no spring vibration system, the micromanipulator is able tofollow rapid movements with good response. The characteristics of themicromanipulator are thus markedly improved over those of the prior artmicromanipulators.

The above and other features of the present invention will becomeapparent from the following description made with reference to thedrawings.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a perspective view showing the overall configuration of themicromanipulator according to the present invention.

FIG. 2 is a plan view showing the configuration of a hand module of themicromanipulator of FIG. 1.

FIG. 3 is a side view, partially broken away, showing the configurationof an essential portion of the hand module of FIG. 2.

FIG. 4 is a sectional view showing how the links of a hand module areconnected.

FIG. 5 is a block diagram of a micromanipulator control system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The overall configuration of an embodiment of the micromanipulatoraccording to the invention is shown in FIG. 1, and the configuration ofthe essential portion of the hand modules 1 constituting the manipulatoris shown in FIGS. 2 and 3.

As shown in FIG. 1, the micromanipulator is constituted as a two-figuremicrohand consisting of two hand modules. In order to realize aprecision mechanism with multiple degrees of freedom, the hand modules 1are equipped with parallel linkages with six degrees of freedom, asshown in FIGS. 2 and 3. Each hand module 1 consists mainly of a circularbase plate 2, an end-effector 3 constituted of a circular moving plate 4of smaller diameter than the base plate 2 and a finger 5 attached to themoving plate 4, and six links 6 that interconnect the base plate 2 andthe moving plate 4.

More specifically, as shown in FIG. 2, the base plate 2 is providedalong its edge with three substantially equally spaced connection points16 for the links 6, and the moving plate 4 is provided along its edgewith three substantially equally spaced connection points 17 offsetabout 60 degrees from the connection points 16 of the base plate.

FIG. 4 shows a specific example of means for connecting the links 6 withthe connection points 16, 17. As illustrated, one end of a bent flexiblemetal wire member 11 is bonded in a hole 9 at either end of each link 6.The other end of the flexible metal wire member 11 at one end of thelink 6 is bonded in a hole 10 of a fastener pin 7 for attachment to thebase plate 2 and the other end of the flexible metal wire member 11 atthe other end of the link 6 is bonded in a hole 10 of a fastener pin 8for attachment to the moving plate 4. Two holes for anchoring twofastener pins 7 are formed at each connection point 16 of the base plate2 and two holes for anchoring two fastener pin 8 are formed at eachconnection point 17 of the moving plate 4. The fastener pins 7, 8 areinserted into the holes formed at the connection points of the baseplate 2 and the moving plate 4 so that at each connection point theassociated two links 6 are inclined in different directions. Thefastener pins 7, 8 are fixed in the holes by screws 12. As a result, thebase plate 2 and the moving plate 4 are connected in parallel by thepairs of flexible metal wire members 11 via the links 6.

Since the actuators (the piezoelectric elements 15 described later)provided on the links extend/contract only by about 1/1000 of theirlength, the flexible metal wire members 11 bend only to a very smallextent. The material selected for the metal wire members therefore doesnot have to be one capable of large bending but needs only to be amaterial whose strength against exterior forces is sufficient forensuring the strength of the manipulator. An example of a materialmeeting this description is steel wire.

The micromanipulator using the aforesaid parallel linkage has to becapable of positioning with multiple degrees of freedom. To this end,each of the six links 6 is equipped with an actuator consisting of astacked piezoelectric element 15 by which it can be extended andcontracted.

While the stacked piezoelectric elements 15 used for precise positioningexhibit rapid response, fine displacement and high output, their verylarge hysteresis makes it impossible to attain accurate positioning onlyby open-loop control of the drive voltage. It is therefore preferable touse feedback control based on measured displacement. For this, it isnecessary to provide the micromanipulator with compact displacementmeasurement means and a servo drive system.

For measuring the position and attitude of the end-effector 3 asrequired in this type of drive control, a strain gage 18 is directlybonded on the side of each stacked piezoelectric element 15 to extend inthe direction of its elongation. The small displacements measured by thestrain gages 18 are fed back and compared with the end-effector 3position and attitude command values and, based on the results of thecomparison, outputs for precision servo positioning control areforwarded to the piezoelectric element 15 drivers.

The servo system for the drive control of the piezoelectric elements 15may, for example, be a software servo system using a computer or ananalog servo system employing operational amplifiers.

FIG. 5 shows an example of the micromanipulator control system. In theillustrated system, a drive signal for the piezoelectric element 15 isoutput by a D/A converter 20 to an analog servo controller 22 whichcorrects the drive signal for the deviation of the link displacementfrom the set value determined on the basis of a signal fed back from thestrain gage 18 via a gage bridge 23 and an instrument amplifier 24 andthe corrected drive signal is sent to the piezoelectric elements 15through a driver 19 constituted as a noninverting amplifier employing ahigh-voltage operational amplifier. Actual link displacements are sentto an A/D converter 21 to be monitored in the digital computer 25.

Tests conducted using a software servo showed that precision andresponse speed adequate for the actuators of the hand modules could beachieved with a relatively simple drive control system.

High response speed can be achieved by basing the analog servoconfiguration on a PID controller.

By selectively driving the piezoelectric elements 15 of themicromanipulator constituted in the foregoing manner so as toextend/contract the links 6, the position and direction of theend-effector 3 can be controlled with six degrees of freedom inaccordance with the amount of extension/contraction of the individuallinks. The micromanipulator can therefore be operated to execute desiredmotions by selective extension/contraction of the links 6.

The micromanipulator according to the invention was fabricated usinghand modules with a base plate 2 about 35 mm in diameter, a moving plate4 about 20 mm in diameter, a spacing between the base plate and themoving plate of about 6 mm, 2×3×10 mm piezoelectric elements 15, amaximum displacement of 8 μm, a finger about 50 mm in length, linksabout 23 mm in length (including the piezoelectric elements), and metalwire members 11 made of steel wire measuring 0.5 mm in diameter. Themotion of the tips of the fingers could be precisely controlled formanipulating minute objects on the several μm order to conduct suchoperations as gripping, positioning, cutting, stretching, mixing and thelike.

The micromanipulator according to this invention achieves an improvementon the micromanipulation characteristics of prior art micromanipulatorswithout sacrificing compactness. Being constituted as a two-fingermicromanipulator utilizing a pair of hand modules comprising parallellinkages with six degrees of freedom, it is strong enough not tostructurally break down easily under external force and, having nospring vibration system, is able to follow rapid movements with goodresponse.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

Japanese Patent Application No. 5-142716 filed May 21, 1993 is herebyincorporated by reference.

What is claimed is:
 1. A micromanipulator comprising a pair of handmodules each comprising:a circular base plate provided along its edgewith three substantially equally spaced connection points, anend-effector consisting of a circular moving plate and a finger attachedto the moving plate, the moving plate being disposed above the baseplate and being provided along its edge with three substantially equallyspaced connection points offset about 60 degrees from the connectionpoints of the base plate, six metal links disposed between the baseplate and the moving plate, six piezoelectric elements provided one oneach of the six metal links for extending and contracting the metallinks, six flexible first metalwire members each connected between oneend of one of the six metal links and one of the three connection pointsof the base plate, two first metal wire members being connected witheach connection point of the base plate to be inclined in differentdirections from each other, and six flexible second metal wire memberseach connected between the other end of one of the six metal links andone of the three connection points of the moving plate, two second metalwire members being connected with each connection point of the movingplate to be inclined in different directions from each other.
 2. Amicromanipulator according to claim 1, further comprising strain gagesbonded one on the side of each actuator to extend in the direction ofits extension/contraction, the detection values from the strain gagesbeing fed back for correcting drive signals supplied to the actuators.